Method of processing a wafer

ABSTRACT

A method of processing a wafer includes a grinding step of grinding a wafer that has first insulating films covering via electrodes, from a reverse side thereof, an electrode protruding step of protruding the via electrodes covered with the first insulating films from the reverse side by way of etching, a distorted layer forming step of forming a distorted layer on the reverse side of the wafer, an insulating film forming step of forming a second insulating film on the reverse side of the wafer, and an electrode forming step of removing the first insulating films and the second insulating film from the regions where they overlap the via electrodes, and forming reverse-side electrodes connected to the via electrodes.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a method of processing a wafer with via electrodes embedded therein.

Description of the Related Art

Device chips incorporated in electronic equipment are fabricated by establishing a plurality of intersecting projected dicing lines on the face side of a wafer made of a semiconductor material or the like, forming devices in respective areas demarcated by the projected dicing lines, and dividing the wafer along the projected dicing lines. In recent years, there have been demands for low-profile device chips to make themselves into a space saver. To meet such demands, before a wafer with devices formed in respective demarcated areas thereof is divided, the wafer is ground on its reverse side to thin itself to a predetermined finished thickness. In addition, it has been desired to reduce the size of areas where device chips are to be installed on given objects and also to attain higher performance in device chips. One solution is to produce a package chip by layering a plurality of device chips and housing the stack in one package.

Heretofore, the plurality of device chips included in the package chip are connected together by wire bonding or the like. The package has been relatively large as it requires an additional space for accommodating bonding wires that interconnect the device chips. As a result, efforts to produce multi-layer assemblies of device chips with bonding wires have had limitations. There has been developed a technology in which via electrodes, i.e., through-electrodes, extending through the device chips in the thicknesswise directions of device chips are formed in the device chips, and the device chips are interconnected by the via electrodes. For example, a technology in which via electrodes formed in device chips divided from a silicon wafer are used to interconnect upper and lower device chips is referred to as through-silicon via (TSV). As the via electrodes can be made shorter than bonding wires, the TSV technology contributes to speeding up of the processing operation of package chips.

Device chips with via electrodes are fabricated according to the following procedure. First, a disk-shaped wafer is prepared. Then, before or after devices are formed on the wafer, via electrodes are embedded into the wafer from its face side to a predetermined depth in excess of the finished thickness of device chips in respective areas demarcated by projected dicing lines. In order to insulate the via electrodes and the wafer from each other and due to circumstances of the process of forming the via electrodes, insulating films such as silicon oxide films or the like are formed on the inner wall surfaces of via holes in which the via electrodes are embedded. Then, the wafer is ground on its reverse side, and thereafter, the via electrodes are exposed on the reverse side of the wafer. Furthermore, electrodes or bumps are formed as terminals on the exposed portions of the via electrodes, after which the wafer is divided along the projected dicing lines (see Japanese Patent Laid-Open No. 2014-33160).

SUMMARY OF THE INVENTION

For exposing the via electrodes embedded in the wafer on the reverse side thereof, an infrared radiation or the like that has a wavelength transmittable through the material of the wafer is applied to the wafer from its reverse side to detect the distance or depth between the bottoms of the via electrodes and the reverse side of the wafer. Then, the wafer is ground on the reverse side to the extent that the insulating films covering the via electrodes will not be exposed. Moreover, the reverse side of the wafer is etched to thin the wafer to the finished thickness of the device chips and at the same time to cause the via electrodes covered with the insulating film to protrude from the reverse side of the wafer. Thereafter, a silicon nitride film is formed on the reverse side of the wafer as a gettering layer for preventing metal elements, etc. from being diffused into the wafer, i.e., the device chips, from outside, and then a silicon oxide film is formed on the reverse side of the wafer as a passivation film. Subsequently, the gettering layer overlapping the via electrodes, the passivation film, and the insulating films covering the via electrodes are removed by chemical mechanical polishing (CMP), thereby exposing the via electrodes on the reverse side of the wafer. Then, electrodes or bumps are formed as terminals on the exposed via electrodes.

Since the device chips with the via electrodes are produced through a number of steps, as described above, the manufacturing cost of the device chips tends to be high. Accordingly, there are demands for simplifying the steps. For example, as the step of forming the silicon nitride film as the gettering layer is highly costly, it is desirable to dispense with the step in order to reduce the manufacturing cost of the device chips.

It is therefore an object of the present invention to provide a method of processing a wafer at a lower cost by simplifying steps of processing the wafer with via electrodes embedded therein to produce device chips with the via electrodes.

In accordance with an aspect of the present invention, there is provided a method of processing a wafer, including the steps of: placing a protective member on a face side of a wafer having a plurality of intersecting projected dicing lines thereon that demarcate the face side into areas with devices formed therein, the areas having via electrodes embedded in the wafer and extending in thicknesswise directions, and first insulating films covering the via electrodes; holding a protective member side of the wafer on a chuck table and grinding the wafer on a reverse side thereof to an extent that the first insulating films covering the via electrodes are not exposed; after the step of grinding the wafer, housing the wafer in a first vacuum chamber, supplying a first etching gas turned to a plasma to the reverse side of the wafer to etch the reverse side, thereby protruding the via electrodes covered with the first insulating films from the reverse side of the wafer; after the step of protruding the via electrodes, supplying an inactive gas turned to a plasma to the reverse side of the wafer from which the via electrodes protrude, thereby forming a distorted layer on the reverse side of the wafer; after the step of forming the distorted layer, forming a second insulating film on the reverse side of the wafer with the distorted layer formed thereon; and after the step of forming the second insulating film, removing the first insulating films and the second insulating film from regions where the first insulating films and the second insulating film overlap the via electrodes, and forming reverse-side electrodes that are connected to the via electrodes exposed on the reverse side of the wafer.

Preferably, the step of forming the distorted layer includes the steps of keeping the wafer housed in the first vacuum chamber from the step of protruding the via electrodes, discharging the first etching gas from the first vacuum chamber, and then supplying the inactive gas turned to a plasma to the first vacuum chamber.

Alternatively, preferably, the method of processing a wafer further includes the steps of, after the step of protruding the via electrodes and before the step of forming the distorted layer, housing the wafer in a second vacuum chamber, supplying a second etching gas turned to a plasma to the reverse side of the wafer to remove a natural oxide film on the reverse side of the wafer, in which the step of forming the distorted layer includes the steps of keeping the wafer housed in the second vacuum chamber, discharging the second etching gas from the second vacuum chamber, and supplying the inactive gas turned to a plasma to the second vacuum chamber.

In the method of processing a wafer according to the aspect of the present invention, the wafer that has the via electrodes covered with the first insulating films is ground from the reverse side thereof, after which the first etching gas turned to the plasma is supplied to etch the reverse side of the wafer, thereby protruding the via electrodes from the reverse side of the wafer. Thereafter, the inactive gas turned to the plasma is supplied to the reverse side of the wafer from which the via electrodes protrude, thereby forming the distorted layer on the reverse side of the wafer. Since the distorted layer functions as a gettering layer for trapping metal elements that tend to enter the wafer from outside, it is not necessary to grow a silicon nitride film functioning as a gettering layer, resulting in simplified steps. Thereafter, the wafer with the distorted layer functioning as the gettering layer is divided along the projected dicing lines into individual device chips that have the via electrodes.

According to the aspect of the present invention, the method of processing a wafer is made less costly by simplifying the steps of processing the wafer with the via electrodes embedded therein to manufacture device chips that have the via electrodes.

The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view schematically illustrating a wafer;

FIG. 1B is a fragmentary perspective view schematically illustrating the wafer at an enlarged scale;

FIG. 2A is a perspective view schematically illustrating a protective member placing step;

FIG. 2B is a cross-sectional view schematically illustrating the manner in which the depths of via electrodes are measured;

FIG. 3A is a cross-sectional view schematically illustrating a grinding step;

FIG. 3B is a fragmentary cross-sectional view schematically illustrating at an enlarged scale the wafer after the grinding step has been carried out thereon;

FIG. 4 is a cross-sectional view schematically illustrating a plasma etching apparatus;

FIG. 5A is a cross-sectional view schematically illustrating the wafer fixed to a table in an electrode protruding step;

FIG. 5B is a fragmentary cross-sectional view schematically illustrating at an enlarged scale the wafer after the electrode protruding step has been carried out thereon;

FIG. 6A is a cross-sectional view schematically illustrating the wafer fixed to the table in a distorted layer forming step;

FIG. 6B is a fragmentary cross-sectional view schematically illustrating at an enlarged scale the wafer after the distorted layer forming step has been carried out thereon;

FIG. 7A is a fragmentary cross-sectional view schematically illustrating at an enlarged scale the wafer on which an insulating film forming step has been carried out;

FIG. 7B is a fragmentary cross-sectional view schematically illustrating at an enlarged scale the wafer from which first insulating films and a second insulating film have been removed from the regions where they overlap the via electrodes;

FIG. 7C is a fragmentary cross-sectional view schematically illustrating at an enlarged scale the wafer on which an electrode forming step has been carried out;

FIG. 8A is a flowchart illustrating an example of a method of processing a wafer; and

FIG. 8B is a flowchart illustrating another example of a method of processing a wafer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A method of processing a wafer according to a preferred embodiment of the present invention will be described below with reference to the accompanying drawings. First, a wafer as a workpiece to be processed by the method of processing a wafer according to the present embodiment will be described below with reference to FIGS. 1A and 1B. FIG. 1A schematically illustrates in perspective the wafer, denoted by 1, and FIG. 1B schematically illustrates in fragmentary perspective the wafer 1 at an enlarged scale. The wafer 1 is a substantially disk-shaped substrate or the like made of a semiconductor material such as silicon (Si), silicon carbide (SiC), gallium nitride (GaN), gallium arsenide (GaAs), or the like, or a material such as sapphire, glass, quartz, or the like.

A plurality of intersecting projected dicing lines 3 are established in a face side 1 a of the wafer 1, demarcating the face side 1 a into areas where devices 5 such as integrated circuits (ICs), large scale integrated (LSI) circuits, or the like are formed. The wafer 1 will subsequently be divided along the projected dicing lines 3 into device chips that include the devices 5. In recent years, for making the device chips thin, it is customary to process the wafer 1 on a reverse side 1 b thereof to thin the wafer 1 to a predetermined finished thickness before the wafer 1 is divided into the device chips. Furthermore, in order to attain higher performance in the device chips and also to reduce the size of areas where the device chips are to be installed on given objects, a package chip is formed by layering a plurality of device chips and housing the stack of device chips in one package. The layered device chips in the package chip are electrically connected to each other by via electrodes or through-electrodes extending through the device chips in the thicknesswise directions thereof, for example.

Each of the areas of the wafer 1 that are demarcated by the projected dicing lines 3, i.e., each of the areas where the device 5 is formed, has via electrodes 9 embedded therein that extend in the thicknesswise directions of the wafer 1 as illustrated in FIG. 1B. The via electrodes 9 are connected to electrodes 7 of the device 5. The via electrodes 9 are embedded to a thickness in excess of the finished thickness of a single device chip. Thereafter, the wafer 1 is thinned to the finished thickness, thereby exposing the via electrodes 9 on the reverse side, and then electrodes or bumps are formed as terminals on the exposed via electrodes 9. Next, the wafer 1 is divided along the projected dicing lines 3 into the device chips that have the devices 5. When a package chip is formed by layering a plurality of device chips, the devices 5 of the device chips are electrically connected to each other by the via electrodes 9 thereof.

The via electrodes 9 are embedded in the wafer 1 before or after the devices 5 are formed. For embedding the via electrodes 9, recesses called via holes for embedding the via electrodes 9 therein are formed in the face side 1 a of the wafer 1 at predetermined positions in the areas of the wafer 1 that are demarcated by the projected dicing lines 3. The via holes are formed to a depth in excess of the finished thickness of the device chips. First insulating films 13 (see FIG. 3B, etc.) are deposited on bottom and inner wall surfaces of the via holes. The first insulating films 13 may be silicon oxide films, for example, and formed by chemical vapor deposition (CVD) or the like. Then, Cu, W, Al, polysilicon, or the like is placed in the via holes, thereby forming the via electrodes 9. Thereafter, the reverse side 1 b of the wafer 1 is processed to thin the wafer 1 until the via electrodes 9 are exposed on the reverse side 1 b.

Next, an example of a plasma treating apparatus used in the method of processing a wafer according to the present embodiment will be described below. The plasma treating apparatus supplies the reverse side 1 b of the wafer 1 with an etching gas turned to a plasma, thereby etching the reverse side 1 b of the wafer 1. In addition, an inactive gas turned to a plasma is supplied to the reverse side 1 b of the wafer 1, thereby forming a distorted layer on the reverse side 1 b of the wafer 1. FIG. 4 is a cross-sectional view schematically illustrating an example of a configuration of the plasma treating apparatus, denoted by 16.

As illustrated in FIG. 4, the plasma treating apparatus 16 includes a first vacuum chamber 20 that defines a treatment space 18 therein. The first vacuum chamber 20 is in the shape of a rectangular parallelepiped including a bottom wall 20 a, an upper wall 20 b, a first side wall 20 c, a second side wall 20 d, a third side wall 20 e, and a fourth side wall, not illustrated. The second side wall 20 d has an opening 22 defined therein through which the wafer 1 can be loaded into and unloaded out of the treatment space 18. A gate 24 for selectively opening and closing the opening 22 is disposed on an outer side surface of the side wall 20 d. The gate 24 is vertically movable by an opening and closing mechanism 26. The opening and closing mechanism 26 includes an air cylinder 28 and a piston rod 30 extending upwardly from the air cylinder 28. The air cylinder 28 is fixed to the bottom wall 20 a of the first vacuum chamber 20 by a bracket 32. The piston rod 30 has an upper distal end coupled to a lower portion of the gate 24.

When the opening and closing mechanism 26 opens the gate 24, the wafer 1 can be loaded through the opening 22 into the treatment space 18 in the first vacuum chamber 20 or can be unloaded through the opening 22 out of the treatment space 18. The bottom wall 20 a of the first vacuum chamber 20 has a discharging port 34 defined therein that is connected to a discharging mechanism 36 such as a vacuum pump or the like. The treatment space 18 in the first vacuum chamber 20 houses therein a lower electrode 38 and an upper electrode 40 that are disposed in vertically facing relation to each other. The lower electrode 38 is made of an electrically conductive material, and includes a disk-shaped holder 42 and a cylindrical support 44 projecting downwardly from a central region of the lower surface of the holder 42. The support 44 is inserted through an opening 46 defined in the bottom wall 20 a of the first vacuum chamber 20. An annular insulator 48 is disposed in the opening 46 between the bottom wall 20 a and the support 44, insulating the first vacuum chamber 20 and the lower electrode 38 from each other. The lower electrode 38 is electrically connected to a high-frequency power supply 50 disposed outside of the first vacuum chamber 20.

The holder 42 has a cavity defined in the upper surface thereof, and a table 52 for placing the wafer 1 thereon is disposed in the cavity. The table 52 has a suction channel, not illustrated, defined therein that is connected to a suction source 56 through a flow channel 54 defined in the lower electrode 38. The holder 42 also has a cooling flow channel 58 defined therein. The cooling flow channel 58 has an end connected to a coolant circulating mechanism 62 through a coolant introducing channel 60 defined in the support 44. The other end of the cooling flow channel 58 is connected to the coolant circulating mechanism 62 through a coolant discharging channel 64 defined in the support 44. When the coolant circulating mechanism 62 is actuated, a coolant flows successively through the coolant introducing channel 60, the cooling flow channel 58, and the coolant discharging channel 64, thereby cooling the lower electrode 38.

The upper electrode 40 is made of an electrically conductive material, and includes a disk-shaped gas ejector 66 and a cylindrical support 68 projecting upwardly from a central region of the upper surface of the gas ejector 66. The support 68 is inserted through an opening 70 defined in the upper wall 20 b of the first vacuum chamber 20. An annular insulator 72 is disposed in the opening 70 between the upper wall 20 b and the support 68, insulating the first vacuum chamber 20 and the upper electrode 40 from each other. The upper electrode 40 is electrically connected to a high-frequency power supply 74 disposed outside of the first vacuum chamber 20. A support arm 78 is mounted on an upper end portion of the support 68 and coupled to a lifting and lowering mechanism 76. The upper electrode 40 is vertically movable by the lifting and lowering mechanism 76 and the support arm 78.

The gas ejector 66 has a plurality of ejection ports 80 defined in a lower surface thereof. The ejection ports 80 are connected to a first gas supply 86 and a second gas supply 88 through a flow channel 82 defined in the gas ejector 66 and a flow channel 84 defined in the support 68. The first gas supply 86, the second gas supply 88, the flow channels 82 and 84, and the ejection ports 80 jointly make up a gas introducing assembly for introducing a gas into the first vacuum chamber 20. The gas supplies of the gas introducing assembly of the plasma treating apparatus 16 are not limited to the two gas supplies 86 and 88.

The opening and closing mechanism 26, the discharging mechanism 36, the high-frequency power supply 50, the suction source 56, the coolant circulating mechanism 62, the high-frequency power supply 74, the lifting and lowering mechanism 76, the first gas supply 86, and the second gas supply 88, etc. are electrically connected to a controller 90. The controller 90 may be in the form of a computer including a processor such as a central processing unit (CPU) and a storage apparatus such as a flash memory, etc. The central processing unit functions as the controller 90 when it executes programs stored in the storage apparatus. The discharging mechanism 36 supplies information associated with the pressure in the treatment space 18 to the controller 90. The coolant circulating mechanism 62 supplies information associated with the temperature of the coolant, i.e., information associated with the temperature of the lower electrode 38, to the controller 90. Furthermore, the first gas supply 86 and the second gas supply 88 supply information associated with the flow rates of gases flowing therefrom to the controller 90. The controller 90 outputs control signals for controlling the various components referred to above on the basis of the supplied information and other information entered by the user of the plasma treating apparatus 16.

The method of processing a wafer according to the present embodiment will be described below with reference to FIG. 8A. FIG. 8A is a flowchart illustrating an example of the method of processing a wafer according to the present embodiment. In the method of processing a wafer according to the present embodiment, the protective member placing step S1 is carried out first. FIG. 2A schematically illustrates the protective member placing step S1 in perspective. In the protective member placing step S1, a protective member 11 is placed on the face side 1 a of the wafer 1. The protective member 11 functions to protect the devices 5, etc. on the face side 1 a of the wafer 1 while the method of processing a wafer according to the present embodiment is being carried out on the wafer 1. The protective member 11 is in the form of a circular adhesive tape having substantially the same diameter as the wafer 1, for example. In the protective member placing step S1, the adhesive tape is stuck to the face side 1 a of the wafer 1. The protective member 11 may alternatively be a rigid circular plate made of a material such as glass, resin, ceramics, or the like. In the case where the protective member 11 is a rigid circular plate, it is stuck to the face side 1 a of the wafer 1 by an adhesive.

After the protective member placing step S1, the grinding step S2 is performed. In the grinding step S2, the wafer 1 is ground on the reverse side 1 b thereof. For performing the grinding step S2, the depths from the reverse side 1 b to the distal ends of the via electrodes 9 are measured in advance. Thereafter, the wafer 1 is ground on the reverse side 1 b thereof while referring to the measured values of the depths, thereby thinning the wafer 1 to the extent that the via electrodes 9 and the first insulating films 13 (see FIG. 3B, etc.) will not be exposed. FIG. 2B schematically illustrates in cross section the manner in which the depths of the via electrodes 9 are measured. As illustrated in FIG. 2B, the wafer 1 is placed on a chuck table 4 with the face side 1 a thereof facing downwardly. Then, a height detecting unit 2 disposed above the chuck table 4 is used to measure the depths of the distal ends of the via electrodes 9. The height detecting unit 2 and the chuck table 4 are included in a grinding apparatus (see FIG. 3A) to be described below, for example. Alternatively, the height detecting unit 2 and the chuck table 4 may be included in an external height measuring apparatus. For example, the height detecting unit 2 is an infrared camera unit that applies an infrared radiation having a wavelength transmittable through the wafer 1 to the reverse side 1 b thereof while moving over the wafer 1, and observes a reflected infrared radiation from the wafer 1 to measure the depths of the via electrodes 9 from the reverse side 1 b.

Next, the grinding apparatus for grinding the wafer 1 will be described below with reference to FIG. 3A. FIG. 3A schematically illustrates the grinding step S2 in cross section. The grinding apparatus, denoted by 6, illustrated in FIG. 3A includes the chuck table 4 and a grinding unit 6 a disposed above the chuck table 4.

The chuck table 4 has an upper surface as a holding surface where a porous material is exposed. The chuck table 4 has a suction channel, not illustrated, defined therein that has an end connected to the porous material of the holding surface and another end connected to a suction source, not illustrated. The wafer 1 is placed on the holding surface of the chuck table 4 with the face side 1 a facing downwardly, and the suction source is actuated to apply a negative pressure to the wafer 1 through the suction channel and the porous material. The wafer 1 is now held under suction on the chuck table 4. The chuck table 4 is rotatable about a central axis perpendicular to the holding surface. The grinding unit 6 a disposed above the chuck table 4 includes a spindle 8 whose central axis extends perpendicularly to the holding surface of the chuck table 4, a wheel mount 10 fixed to the lower end of the spindle 8, and a grinding wheel 12 mounted on a lower surface of the wheel mount 10. A grinding stone 14 is mounted on a lower surface of the grinding wheel 12. The upper end of the spindle 8 is connected to a rotary actuator, not illustrated. When the rotary actuator is energized, it rotates the spindle 8 about its central axis, rotating the grinding wheel 12 to cause the grinding stone 14 to move along a circular orbit.

In the grinding step S2, the chuck table 4 and the spindle 8 are rotated independently of each other, and the grinding unit 6 a is lowered. When the grinding stone 14 that is moving along the circular orbit is lowered into contact with the reverse side 1 b of the wafer 1 held on the chuck table 4, the wafer 1 is ground by the grinding stone 14. The grinding unit 6 a is lowered to a predetermined vertical position where the via electrodes 9 and the first insulating films 13 (see FIG. 3B, etc.) in the wafer 1 will not be exposed. FIG. 3B schematically illustrates the wafer 1 after the grinding step S2 has been carried out thereon in fragmentary cross section. As illustrated in FIG. 3B, in the grinding step S2, the wafer 1 is ground on the reverse side 1 b to the extent that the insulating films 13 covering the via electrodes 9 a will not be exposed on the reverse side 1 b.

The disk-shaped wafer 1 made of Si or the like has an outer circumferential edge beveled beforehand to prevent itself from being chipped away. Therefore, the face side 1 a and reverse side 1 b of the wafer 1 are joined to each other by a curved side surface around the outer circumferential edge. When the wafer 1 is ground on the reverse side 1 b in the grinding step S2, the outer circumferential edge of the wafer 1 tends to be sharpened into a knife edge, which is likely to cause the wafer 1 to be chipped away. To avoid such a shortcoming, an edge trimming process may be carried out on the wafer 1 to remove the outer circumferential edge of the wafer 1 before the wafer 1 is ground.

In the method of processing a wafer according to the present embodiment, the grinding step S2 is followed by the electrode protruding step S3 for protruding the via electrodes 9 covered with the first insulating films 13 from the reverse side 1 b of the wafer 1. The electrode protruding step S3 is carried out by the plasma treating apparatus 16 illustrated in FIG. 4, for example. In the electrode protruding step S3, the opening and closing mechanism 26 lowers the gate 24 of the plasma treating apparatus 16. Then, the wafer 1 is loaded through the opening 22 into the treatment space 18 in the first vacuum chamber 20, and placed on the table 52 of the lower electrode 38 with the reverse side 1 b exposed upwardly. When the wafer 1 is loaded into the treatment space 18, it is preferable to actuate the lifting and lowering mechanism 76 to lift the upper electrode 40, thereby widening the distance between the lower electrode 38 and the upper electrode 40.

Thereafter, the vacuum pressure from the suction source 56 is applied to attract the wafer 1 under suction securely to the table 52. The opening and closing mechanism 26 lifts the gate 24 to seal the treatment space 18. The lifting and lowering mechanism 76 adjusts the vertical position of the upper electrode 40 to bring the upper electrode 40 and the lower electrode 38 into a predetermined positional relationship suitable for plasma processing. The discharging mechanism 36 is actuated to evacuate the treatment space 18 to a lower pressure. FIG. 5A schematically illustrates in cross section the wafer 1 introduced into the plasma treating apparatus 16 in the electrode protruding step S3. After the treatment space 18 has been evacuated, if it is difficult to hold the wafer 1 on the table 52 under the negative pressure from the suction source 56, then the wafer 1 may be held on the table 52 by electric forces, typically electrostatic forces, or the like. For example, an electrode may be embedded in the table 52, and electric power may be supplied to the electrode to apply electric forces between the table 52 and the wafer 1.

Then, while a gas for plasma processing, including a first etching gas, is being introduced from the first gas supply 86 into the treatment space 18 at a predetermined flow rate, predetermined high-frequency electric power is applied between the lower electrode 38 and the upper electrode 40. The first etching gas is CF₄ or SF₆, for example. The first etching gas is mixed with a hydrogen gas, an oxygen gas, or the like at a predetermined ratio before it is introduced into the treatment space 18. In the electrode protruding step S3, while a predetermined pressure ranging from 5 to 50 Pa, for example, is being maintained in the treatment space 18, the first etching gas is supplied from the first gas supply 86 at the predetermined flow rate to the treatment space 18, and predetermined high-frequency electric power ranging from 1000 to 3000 W, for example, is applied between the lower electrode 38 and the upper electrode 40.

Now, a plasma is generated between the lower electrode 38 and the upper electrode 40, and ions produced from the first etching gas turned to the plasma are attracted toward the lower electrode 38 and supplied to the reverse side 1 b of the wafer 1. The supplied ions etch the reverse side 1 b at a high selection ratio between the wafer 1 and the first insulating films 13. Specifically, when the electrode protruding step S3 is performed, the wafer 1 is gradually etched away, whereas the first insulating films 13 as they are exposed are less likely to be etched away. Therefore, when the electrode protruding step S3 is performed, as illustrated in FIG. 5B, the reverse side 1 b of the wafer 1 is etched away or retracted, thereby leaving the via electrodes 9 and the first insulating films 13 protruding from the reverse side 1 b of the wafer 1. FIG. 5B schematically illustrates in fragmentary cross section the wafer 1 after the electrode protruding step S3 has been carried out thereon.

In the method of processing a wafer according to the present embodiment, then, the distorted layer forming step S4 is carried out to form a distorted layer on the reverse side 1 b of the wafer 1 by supplying an inactive gas turned to a plasma to the reverse side 1 b with the via electrodes 9 protruding therefrom. The distorted layer forming step S4 may be carried out in the first vacuum chamber 20 following the electrode protruding step S3 while the wafer 1 remains housed in the first vacuum chamber 20 from the electrode protruding step S3. In this case, after the first etching gas has been discharged, the inactive gas turned to the plasma is introduced into the first vacuum chamber 20. FIG. 6A schematically illustrates in cross section the wafer 1 fixed to the table 52 in the first vacuum chamber 20 in the distorted layer forming step S4.

In the distorted layer forming step S4, while the inactive gas for plasma process is being supplied at a predetermined flow rate to the wafer 1 fixed to the table 52, predetermined high-frequency electric power is applied between the lower electrode 38 and the upper electrode 40. In the distorted layer forming step S4, while a predetermined pressure ranging from 5 to 50 Pa, for example, is being maintained in the treatment space 18, an inactive gas such as Ar, He, Ne, or the like is supplied from the second gas supply 88 at the predetermined flow rate to the treatment space 18, and predetermined high-frequency electric power ranging from 1000 to 3000 W, for example, is applied between the lower electrode 38 and the upper electrode 40. Now, a plasma is generated between the lower electrode 38 and the upper electrode 40, and ions produced from the inactive gas turned to the plasma are attracted toward the lower electrode 38 and supplied to the reverse side 1 b of the wafer 1. The supplied ions sputter the reverse side 1 b, forming minute surface irregularities and cracks or distortions on the reverse side 1 b. The region of the reverse side 1 b where the distortions are formed becomes a distorted layer 15.

FIG. 6B schematically illustrates in cross section at an enlarged scale the wafer 1 on which the distorted layer forming step S4 has been carried out. As illustrated in FIG. 6B, when the distorted layer forming step S4 has been carried out, the distorted layer 15 is formed on the reverse side 1 b of the wafer 1. The distorted layer 15 functions as a gettering layer for trapping metal elements that tend to enter the wafer 1 from the reverse side 1 b thereof.

In the method of processing a wafer according to the present embodiment, since the distorted layer 15 that functions as a gettering layer is formed by the distorted layer forming step S4, it is not necessary to perform a film growing step of growing a gettering layer in the form of a silicon nitride film or the like on the reverse side 1 b of the wafer 1. Specifically, when providing the distorted layer forming step S4 is carried out following the electrode protruding step S3, the distorted layer forming step S4 can be performed simply by changing gases supplied to the wafer 1 in the plasma treating apparatus 16 after the electrode protruding step S3 has been performed. In other words, the cost required to carry out the distorted layer forming step S4 in the method of processing a wafer according to the present embodiment is very low, so that a gettering layer can be formed efficiently on the reverse side 1 b of the wafer 1. The steps of manufacturing the device chips having the via electrodes are thus simplified, so that the wafer 1 can be processed with a high processing efficiency.

In the distorted layer forming step S4, the distorted layer 15 is formed by bombarding reverse side 1 b of the wafer 1 with the inactive gas turned to the plasma. In this process, debris may possibly be produced from the wafer 1, and applied to and deposited on the inner wall surfaces of the first vacuum chamber 20. Providing the electrode protruding step S3 and the distorted layer forming step S4 are carried out in the first vacuum chamber 20, after the distorted layer forming step S4, the electrode protruding step S3 is performed on a next wafer in the first vacuum chamber 20. In such the electrode protruding step S3, the first etching gas turned to the plasma is supplied to the reverse side 1 b of the wafer 1 and also reaches the debris deposited on the inner wall surfaces of the first vacuum chamber 20, removing the debris. Therefore, when the electrode protruding step S3 and the distorted layer forming step S4 are carried out on a succession of wafers one by one in the first vacuum chamber 20, since the debris is automatically removed, the frequency of cleaning of the first vacuum chamber 20 for maintenance is lowered, resulting in a higher wafer processing efficiency.

The distorted layer forming step S4 is followed by the insulating film forming step S5. In the insulating film forming step S5, a second insulating film is formed on the reverse side 1 b of the wafer 1 with the distorted layer 15 formed thereon. FIG. 7A schematically illustrates in cross section at an enlarge scale the wafer 1 on which the insulating film forming step S5 has been carried out. In the insulating film forming step S5, a silicon oxide film is formed as a second insulating film 17 on the reverse side 1 b of the wafer 1 by sputtering, CVD, or the like. The second insulating film 17 functions as a passivation film for protecting the reverse side 1 b of the wafer 1.

The electrode forming step S6 is carried out after the insulating film forming step S5. In the electrode forming step S6, the via electrodes 9 are exposed on the reverse side 1 b of the wafer 1, and reverse-side electrodes are formed that are connected to the via electrodes 9. In the electrode forming step S6, prior to the formation of the reverse-side electrodes, the first insulating films 13 and the second insulating film 17 are removed from the regions where they overlap the via electrodes 9. FIG. 7B schematically illustrates in cross section at an enlarge scale the wafer 1 from which the first insulating films 13 and the second insulating film 17 have been removed from the regions where they overlap the via electrodes 9.

The first insulating films 13 and the second insulating film 17 are removed by CMP, for example. The via electrodes 9 that are covered with the first insulating films 13 protrude from the reverse side 1 b of the wafer 1 in the electrode protruding step S3. Therefore, when portions of the via electrodes 9 that protrude from the reverse side 1 b of the wafer 1 are removed by CMP, the first insulating films 13 and the second insulating film 17 that overlap the via electrodes 9 are removed, thereby exposing the via electrodes 9 on the reverse side 1 b. Now, it is possible to form reverse-side electrodes electrically connected to the via electrodes 9. Since major areas of the reverse side 1 b of the wafer 1 are protected by the second insulating film 17, the distorted layer 15 on the reverse side 1 b is not damaged by CMP. Alternatively, the via electrodes 9 may be exposed by photolithography.

Next, electrodes are formed for connection to the via electrodes 9. FIG. 7C schematically illustrates in cross section at an enlarge scale the wafer 1 on which the electrode forming step S6 has been carried out. Electrodes 19 are in the form of bumps made of metal such as Au, Cu, Sn, or the like or a laminate of these metals, for example. For example, the electrodes 19 are formed by pressing a metal wire against the via electrodes 9 and cutting the metal wire into short lengths. Alternatively, a resist film with openings where the via electrodes 9 are exposed may be formed on the reverse side 1 b, and electrodes 19 may be formed on the exposed areas of the via electrodes 9 by electroplating. Thereafter, the wafer 1 is divided into the device chips with the via electrodes 9. The device chips are layered and connected by the via electrodes 9, and then housed in a package, thereby completing a package chip.

In the above embodiment, the electrode protruding step S3 and the distorted layer forming step S4 are successively carried out in the first vacuum chamber 20. However, the present invention is not limited to such details. According to a modification, the electrode protruding step S3 and the distorted layer forming step S4 may not be successively carried out in the first vacuum chamber 20, but another desired process may be carried out on the wafer 1 outside of the vacuum chamber between the electrode protruding step S3 and the distorted layer forming step S4. The distorted layer forming step S4 may be performed by another plasma treating apparatus having a second vacuum chamber. FIG. 8B is a flowchart of steps of a method of processing a wafer according to a modification of the present invention in which the distorted layer forming step S4 is performed by another plasma treating apparatus having a second vacuum chamber. The plasma treating apparatus having the second vacuum chamber has a similar structure to the plasma treating apparatus 16 described above.

During a period of time between unloading the wafer 1 from the plasma treating apparatus 16 having the first vacuum chamber 20 and loading the wafer 1 into the plasma treating apparatus having the second vacuum chamber after the electrode protruding step S3, a natural oxide film may grow on the reverse side 1 b of the wafer 1. Accordingly, the oxide film removing step S7 for removing such a natural oxide film may be carried out after the electrode protruding step S3 and before the distorted layer forming step S4. In the oxide film removing step S7, the wafer 1 is placed in the second vacuum chamber, and a second etching gas turned to a plasma is supplied to the reverse side 1 b of the wafer 1 to remove a natural oxide film that has grown on the reverse side 1 b. The second etching gas is C₄F₆, C₄F₈, or the like, for example, and is mixed with a hydrogen gas or the like at a predetermined ratio before it is supplied to the wafer 1. In subsequent the distorted layer forming step S4, the wafer 1 remains housed in the second vacuum chamber, and the second etching gas is discharged from the second vacuum chamber. Then, an inactive gas turned to a plasma is supplied to the second vacuum chamber. The distorted layer forming step S4 can be carried out simply by changing gases supplied to the wafer 1 in the plasma treating apparatus after the oxide film removing step S7 has been performed. Therefore, the method for processing a wafer can be carried out efficiently.

The present invention is not limited to the details of the above described preferred embodiment. The scope of the invention is defined by the appended claims and all changes and modifications as fall within the equivalence of the scope of the claims are therefore to be embraced by the invention. 

What is claimed is:
 1. A method of processing a wafer, comprising the steps of: placing a protective member on a face side of a wafer having a plurality of intersecting projected dicing lines thereon that demarcate the face side into areas with devices formed therein, the areas having via electrodes embedded in the wafer and extending in thicknesswise directions, and first insulating films covering the via electrodes; holding a protective member side of the wafer on a chuck table and grinding the wafer on a reverse side thereof to an extent that the first insulating films covering the via electrodes are not exposed; after the step of grinding the wafer, housing the wafer in a first vacuum chamber, supplying a first etching gas turned to a plasma to the reverse side of the wafer to etch the reverse side, thereby protruding the via electrodes covered with the first insulating films from the reverse side of the wafer; after the step of protruding the via electrodes, supplying an inactive gas turned to a plasma to the reverse side of the wafer from which the via electrodes protrude, thereby forming a distorted layer on the reverse side of the wafer; after the step of forming the distorted layer, forming a second insulating film on the reverse side of the wafer with the distorted layer formed thereon; and after the step of forming the second insulating film, removing the first insulating films and the second insulating film from regions where the first insulating films and the second insulating film overlap the via electrodes, and forming reverse-side electrodes that are connected to the via electrodes exposed on the reverse side of the wafer.
 2. The method of processing a wafer according to claim 1, wherein the step of forming the distorted layer includes the steps of keeping the wafer housed in the first vacuum chamber from the step of protruding the via electrodes, discharging the first etching gas from the first vacuum chamber, and then supplying the inactive gas turned to a plasma to the first vacuum chamber.
 3. The method of processing a wafer according to claim 1, further comprising the steps of: after the step of protruding the via electrodes and before the step of forming the distorted layer, housing the wafer in a second vacuum chamber, supplying a second etching gas turned to a plasma to the reverse side of the wafer to remove a natural oxide film on the reverse side of the wafer, wherein the step of forming the distorted layer includes the steps of keeping the wafer housed in the second vacuum chamber, discharging the second etching gas from the second vacuum chamber, and supplying the inactive gas turned to a plasma to the second vacuum chamber. 